This invention relates to active devices and, more particularly to active devices formed with threads.
Active devices generally have electrical impedance between two electrodes that varies as a function of a change of energy. For example, active devices include transistors, diodes, strain gauges, electrical optical devices and the like. One form of transistor is the well-known field effect transistor (FET). One known FET is a metal oxide semiconductor FET(MOSFET), which has been widely used as a switching element for high-speed electronic applications. The MOSFET specifically refers to SiO2/bulk silicon transistors. A more general FET is a metal insulator semiconductor FET (MISFET). A thin film transistor (TFT) is a MISFET in which the active semiconductor material is deposited as a thin film.
It is known to fabricate active devices with either crystalline silicon or amorphous silicon. Amorphous silicon is a cheaper alternative to crystalline silicon, but its applications are limited to slower speed devices as its mobility is about 10xe2x88x921 cm2/N*sec, which is about 15,000 times smaller than that of crystalline silicon.
Currently, there is much work directed to developing alternative materials, such as organic and organic-inorganic semiconductor materials that may be deposited by low cost and low temperature processes. Lower processing costs may lead to low cost logic and display devices. Lower temperature processing opens up the possibility of depositing these materials on a wider range of substrates, including plastic, paper and fabrics for flexible electronic devices.
An example of a FET made with organic materials is disclosed in U.S. Pat. No. 5,347,144 to Garnier et al., entitled xe2x80x9cThin-Layer Field Effect Transistors With MIS Structure Whose Insulator and Semiconductor Are Made of Organic Materials.xe2x80x9d Organic materials may provide a less expensive alternative to inorganic materials for TFT structures, as they are cheaper to manufacture by methods, such as spin coating or dip coating from solution, thermal evaporation, or screen printing. Such organic materials include small molecules (e.g., pentacene, metal-phthalocyanines and the like), short-chain oligomers (e.g., n-thiophenes, where n=3-8 thiophene units) and polymers (e.g., polyalkylthiophenes, poly-phenylenevinylenes and the like).
An example of a FET made with organic-inorganic materials is described in U.S. Pat. No. 6,180,956 to Chondroudis et al., entitled xe2x80x9cThin Film Transistors With Organic-Inorganic Hybrid Materials as Semiconducting Channels.xe2x80x9d Again, TFTs made with organic-inorganic materials can use the cheaper manufacturing processes, such as spin coating or dip coating from solution, thermal evaporation, or screen printing.
Conventional active devices are generally formed on planar substrates. Thus, current efforts to make flexible devices are focussed on deposition of the semiconductor devices on large area flexible substrates. These efforts have not yet provided a commercial flexible electronic device.
Accordingly, there is a need for an active device that can be fabricated with low cost and low temperature processing.
There is also a need for an assembly of and a method for forming a plurality of active devices on a flexible substrate.
There is also a need for a method of forming a large area assembly of such active devices.
An active device of the present invention is formed of a thread with a semiconductor body extending axially along the thread. First and second electrical conductors extend axially along the thread and are disposed in electrical contact at spaced apart locations with the semiconductor body. The carrier concentration in the semiconductor body varies with energy that affects the thread, thereby also varying the impedance between the first and second electrical conductors.
According to an aspect of the invention, the thread has an optical fiber core upon which the semiconductor body is disposed and the energy is light energy. According to another aspect of the invention, the thread has a piezo-electric core upon which the semiconductor body is disposed and the energy is mechanical. According to another aspect of the invention, the thread has an electrically conductive core with a layer of electrical insulation upon which the semiconductor body is disposed and the energy is electrical. According to further aspects of the present invention, the energy can be heat or chemical with a suitable core.
According to other aspects of the invention, the active device is formed of a plurality of threads and the semiconductor body that extends axially of one of the threads. Two of the threads are electrically conductive and a third thread is responsive to applied energy to modulate the carrier concentration of the semiconductor body. The third thread can have either an optical fiber core or an electrically conductive core. The semiconductor body can be either a layer that is disposed on the third thread or an elongated body that is disposed in a region between the three threads. When the third thread has an electrically conductive core with a layer of electrical insulation, the active device is a field effect transistor. In these devices current flow is in a path that includes the first and third threads and the semiconductor body. That is, current flow is perpendicular or radial with respect to the axes of the first and second threads.
The threads used to form the various active devices of the present invention are formed of one or more filaments that are flexible or bendable. Thus, the need for a flexible substrate and flexible active device is met by the present invention.
The semiconductor body includes a semiconductor that can be disposed on a thread core that has a layer of electrical insulation disposed thereon, or that is an optical fiber or a piezo-electric material. Preferably, the semiconductor body includes an organic semiconductor or a hybrid organic/inorganic semiconductor or other semiconductor types that can be formed on the thread cores with low cost and low temperature processes, such as spin coating or dip coating from solution, thermal evaporation, or screen printing. Thus, the active devices of the present invention can be made with low cost and low temperature processes, thereby satisfying the aforementioned needs.
According to still another aspect of the present invention, an electrical circuit includes a plurality of threads and at least one semiconductor body with the threads forming two or more active devices. In some of these embodiments, each thread is an active device. In other embodiments, two or more active devices can share an electrically conductive thread.
According to still further aspects of the present invention, a fabric includes a plurality of threads in which at least one of the threads forms an active device.